Exercise

In addition to helping us enjoy a healthier body weight, exercise may also boost our immune system. Studies have found that if we let kids run around for just six minutes, the levels of immune cells circulating in their blood may increase by nearly 50 percent. At the other end of the life cycle, regular exercise may also help prevent age-related immune decline. One study found that while elderly, sedentary women have a 50 percent chance of getting an upper-respiratory illness during the fall season, those randomized to begin a half-hour-a-day walking program dropped their risk down to 20 percent.

Physical activity is also considered a promising preventive measure against breast cancer—not only because it helps with weight control but because exercise tends to lower circulating estrogen levels. Five hours a week of vigorous aerobic exercise may lower estrogen and progesterone exposure by about 20 percent, and moderately intense activity may offer as much benefit as vigorous exercise; walking an hour a day or more appears to be associated with significantly lower breast cancer risk.

Can exercise halt cognitive decline? Researchers took a group of people with mild cognitive impairment (for example, those starting to forget things or regularly repeating themselves) and had them engage in aerobic exercise for 45 to 60 minutes a day, 4 days a week, for 6 months. The control group simply stretched for the same time periods. Researchers found that in the control group, cognitive function appeared to continue to decline. But the exercising group not only didn’t get worse, they seemed to get better, answering more test questions correctly after six months, indicating their memory had improved. Indeed, aerobic exercise may actually reverse age-related shrinkage in the memory centers of the brain and help improve cerebral blood flow, improve memory performance, and help preserve brain tissue.

Exercise may also help prevent and treat high blood pressure, and improve our mood and quality of sleep. If the U.S. population collectively exercised enough to shave just 1 percent off the national body mass index (BMI), 2 million cases of diabetes, 1.5 million cases of heart disease, and up to 127,000 cases of cancer may be prevented.

I recommend 90 minutes of moderate-intensity activity, such as brisk (four miles per hour) walking or 40 minutes of vigorous activity (such as jogging or active sports) each day.